Certain wood species have barks which contain long, relatively strong fibers. For example, in the case of Eucalyptus globulus, the bark of the relatively newly felled trees adheres so loosely to the core of the tree that any debarking tools or cutting knives fail to cut the bark. Instead, bark is pushed in front of the tool, so that the bark leaves the log in the form of long strips which soon block the log handling mechanisms. Drum debarkers employ a large rotating drum with internal surface elements which cut and chip the bark off logs tumbled within the drum. The drum has openings which allow the bark to fall through while the logs are progressed towards the chipper. However, in many cases, particularly with bark containing long fibers, the bark will form balls two or three feet in diameter which are too large to pass through the openings in the drum and which are thus advanced to the chipper. It is undesirable to have bark enter the chipper, because bark-contaminated wood chips will include dark fibers which resist bleaching and which thus lower the grade of paper made from the chips.
Debarking of logs can be particularly difficult in the winter in northern climes because the bark is frozen to the log. Soaking the logs in hot water is of limited effectiveness in thawing the bark. The bark itself resists water, and thus prevents hot water from penetrating into the bark. The bark is somewhat insulative and so, in practice, very little thawing takes place through the bark thickness.
Handling bark removed from certain species is also difficult. The large bark sheets from eucalyptus can plug conveyors and holding bins. Bark sheets may intertwine and adhere to each other, causing blockages, for example creating an entire bin of bark agglomerated into a single mass. To alleviate these blockages, separate bark handling process lines are often used, including a chopping apparatus for reducing the size of the bark pieces. Such apparatuses are expensive and are subject to clogging and mechanical failure during operation.
In the past, complicated pre-treating devices and methods have been used with some log species in an attempt to facilitate bark removal and handling. However, most such devices have generally been prohibitively expensive and operationally ineffective. In some locales bark is still stripped by hand from eucalyptus with resultant high labor costs.
What is needed is a process for conditioning the bark on a log to facilitate its mechanical removal from the log.